The present invention relates to an auto-ranging apparatus for use with photographic cameras for determining the distance-to-subject range and, more particularly, to an auto-ranging apparatus that utilizes infra-red radiation emitted by the subject(s) of principal interest for determining the distance-to-subject range.
Motion picture and still picture cameras are typically focused by manual adjustment of the camera lens while viewing a focus indicator such as the split-image screen provided in so-called range finder cameras and the focusing screen provided in single lens reflex cameras. Automatic focusing systems have been developed which permit the camera to auto focus, that is, determine the distance-to-subject range without intervention of the camera operator. These automatic systems have included, for example, infra-red ranging systems and sonic ranging systems. The infra-red systems typically include a source of infra-red energy which irradiates the subject(s) of principal interest with infra-red radiation. An infra-red responsive sensor measures the radiation reflected from the subject(s) with the output of the sensor used to set the lens focus. In the sonic systems, a pulse of sonic energy is directed in the direction of the subject(s) and the time interval between the transmission of the irradiating pulse and the reception of the reflected energy is measured to determine the distance-to-subject range. Both of these systems are of the active type in that the camera must emit irradiating energy in the general direction of the subject(s) of principal interest in order to determine the subject range.
It is a principal object of the present invention, among others, to provide an auto-ranging system for a still or motion picture camera which accurately and efficiently determines the distance-to-subject range without the need for an irradiating energy source in the camera.
It is another object of the primary invention to provide an auto-ranging system for a camera which is both simple to operate and inexpensive to manufacture.
In accordance with these objects and others, the present invention provides a passive infra-red ranging system for a photographic camera or the like which includes two infra-red responsive sensors spaced apart from one another and oriented in the direction of the scene to be photographed. Each sensor is divided into a plurality of individual infra-red responsive segments with each segment receiving a portion of the radiation emitted from the scene and providing an appropriate output therefrom. In one embodiment, a scanning and computing circuit cyclically and successively scans the segments of both sensors and stores the output information for amplitude comparison to determine the angular relationship between the various segments on both sensors and the subject(s) of principal interest. This angular relationship information is then used to determine the distance-to-subject range by triangulation. In another embodiment of the present invention, one of the two sensors is angularly adjustable relative to the other to permit the camera operator to aim the adjustable sensor in the direction of the subject of principal interest. Scanning circuitry cyclically scans the outputs of the sensor segments and determines when coincidence occurs between the fixed and adjustable sensors to permit computing circuitry to determine the distance-to-subject range by triangulation.
The present invention advantageously permits a camera user to determine the range of the subject(s) of principal interest under low light conditions using energy emitted from the subject itself. The invention is especially useful in low light portraiture and in photographing heat emitting machinery when it is desired to range on the portion thereof having the greatest infra-red energy emission.